Effects of different tree shapes on yield and quality of ‘Luguang’walnut

Abstract:【Objective】The major objectives of this work are to (1) select the most suitable tree shape for high nut yield and quality in early- fruiting walnut‘Luguang’from the 3 commonly used tree shapes including trunk-layered shape, open centre shape and natural round shape; (2) provide references and technical guidance for the cultivation and maintenance of the most suitable tree shape of this walnut variety.【Methods】5-year-old early-fruiting walnut variety‘Luguang’trees were used as the experimen-tal materials to comparatively analyze the canopy structural parameters, average yield per plant, average yield per unit canopy projection area, morphological indexes and nutritional components of walnut from trees with the above mentioned three canopy shapes. The tree height was measured from the ground to the top of the crown with a tower ruler; the trunk base diameter was measured with a tape 20 cm from the ground; and the crown width was measured with a meter ruler at the east-west and northsouth directions of the vertical projection edge of the crown. The vertical diameter, transverse diameter and lateral diameter of the nut were measured with a digital caliper. The average fruit weight, kernel weight and yield per plant were determined with an electronic scale. The contents of protein, crude fat,ascorbic acid, total sugar and amino acid were measured using kjeldahl method, soxhlet extraction meth-od, 2, 4-dinitrophenylhydrazine method, reducing sugar release method, and automatic amino acid ana-lyzer, respectively. Principal component analysis (PCA) was used to comprehensively evaluate the dif- ferent tree shapes.【Results】Results from one-way ANOVA showed that tree shape had significant influ- ence on tree height (p ≤ 0.01), trunk diameter (p ≤ 0.05), number of skeleton branches (p ≤ 0.001), av- erage yield per plant (p ≤ 0.001), average yield per unit canopy projection area (p ≤ 0.001), average fruit weight (p ≤ 0.001), kernel weight (p ≤ 0.01), shell thickness (p ≤ 0.001), kernel rate (p ≤ 0.001),protein content (p ≤ 0.05), crud fat content (p ≤ 0.05), ascorbic acid content (p ≤ 0.01), total sugar con-tent (p ≤ 0.05) and total amino acid content (p ≤ 0.05), but no significant effect of tree shape was ob-served (p > 0.05) on canopy width, fruit vertical, transverse and lateral diameters, fruit shape index, con-tents of the 17 amino acids and total essential amino acid, and the percentage of essential amino acids.Trees with trunk-layered shape had the highest tree height (4.55 m), trunk diameter (11.31 cm), number of skeleton branches (6.25) and average yield per plant (7.12 kg), which were significantly higher than that of the trees with natural round shape (3.78 m, 10.49 cm, 5.25 and 6.47 kg, respectively). Tree height, trunk diameter, number of skeleton branches and average yield per plant of the tree with open centre shape were 4.05 m, 10.79 cm, 5.00 and 6.72 kg, respectively. Trees with open centre shape had the highest canopy width (4.08 m, 4.05 m), followed by trees with natural round shape (4.00 m, 3.88 m) and trunk-layered shape (3.78 m, 3.65 m). The average yield per unit canopy projection area in trees with trunk-layered shape and natural round shape was 0.61 and 0.59 kg·m-2, respectively, both being sig-nificantly higher than that in trees with open centre shape (0.51 kg·m-2, p ≤ 0.05). The highest values in average fruit weight (17.00 g) and kernel weight (9.79 g) were observed in trees with trunk-layered shape, which were significantly higher than those in the round shaped trees (16.03 g and 9.25 g, respec-tively) (p ≤ 0.05). The average fruit weight and kernel weight of walnut in trees with open centre shape was 16.50 g and 9.70 g, respectively, which had no significant difference from those in trees with the other two shapes. Trees with open centre shape showed the lowest shell thickness (1.01 mm) and the highest kernel coverage (58.72%), which were significantly lower and higher respectively than those in trees with trunk-layered shape (1.06 mm and 57.61%, respectively) and natural round shape (1.06 mm and 57.81%, respectively) (p ≤ 0.05). Trees with open centre shape were highest in kernel protein con-tent (172.97 mg·g^{- 1}), which was significantly higher than that in trees with natural round shape (165.09 mg·g^{- 1}) and trunk-layered shape (160.96 mg · g^{- 1}) (p ≤ 0.05). Trees with trunk-layered shape had the highest values in crude fat content (676.93 mg·g^-1) and ascorbic acid content (2.95 mg·g^-1), followed by trees with open centre shape (668.99 and 2.72 mg · g^{- 1}, respectively) and natural round shape (660.92 and 2.40 mg·g^-1, respectively). The total sugar content in the kernel from trees with natural round shape was the highest (17.18 mg·g^-1), followed by those in the open centre shape (16.64 mg·g-1) and trunk-lay-ered shape (15.90 mg · g^-1). Seventeen amino acids were determined in‘Luguang’walnut kernel, among which the seven essential amino acids were detected with a total content in the range from 44.62 to 48.36 mg·g^-1, accounting for 28.26 to 29.32% of the total amino acids. The total amino acids content in the kernel of‘Luguang’walnut was 153.02-164.92 mg · g^-1, and glutamate showed the highest con- tent (29.67-32.29 mg·g^-1), followed by arginine (19.35-21.76 mg·g^-1) and aspartate (16.99-17.58 mg·g^-1),while methionine had the lowest content (1.36-1.60 mg·g^-1). The results of PCA showed that the order of productivity potential among different tree shapes was trunk-layered shape > open centre shape > nat-ural round shape, while the order for quality formation was open centre shape > trunk-layered shape >natural round shape.【Conclusion】Taking productivity and quality into account, the best tree shape for ‘Luguang’walnut is trunk-layered shape, followed by open centre shape and natural round shape.